The invention relates to a microwave hyperthermia applicator for heating a limited environment in a dissipative medium, particularly for heating diseased tissue in the human body.
Hyperthermia as brain tumor therapy places special requirements on the treatment system. High blood flow, particular temperature sensitivity of the healthy brain tissue and the limited possibility for surgical treatment of the tumor necessitate a hyperthermia system which is particularly compact and permits sufficiently high thermal energy deposition in a predetermined and limited region in the brain.
German patent application P 3,831,016.3 (and the corresponding German published patent application DE 3,831,016 A1, published Mar. 15, 1990), discloses microwave hyperthermia applicators, antenna arrangements for locally heating a dissipative medium, the tumor-afflicted human tissue. In this case, the incorporation of line transformers at the end of a coaxial feeder cable for a dipole antenna makes it possible for heating to take place only around the dipole antenna, namely in the diseased human tissue and less along the outer sheath of the feeder cable, namely in the healthy human tissue.
Microwave hyperthermia applicators as disclosed in German Patent Application DE 3,831,016.3 still conduct a considerable portion of electrical energy back over the outer conductor so that the dissipative medium is heated.
Another patent, U.S. Pat. No. 4,700,716, discloses and claims a coaxial applicator arrangement which is excited at a proximal end that is not utilized to heat the environment and is there also provided with a termination including a .lambda./4 sleeve. The thinner region of the subsequent, distal end of the coaxial applicator arrangement then serves to actually heat the environment if the latter is composed of a heatable medium. This applicator is no dipole antenna. Due to the radiation characteristic, it is not possible to heat a narrowly defined region by electromagnetic radiation as precisely as with the dipole antenna arrangement according to the invention.